Your wallet can be real pain for your back and the waist, and it can even lead to shooting pains down the legs. Sitting on a wallet for prolonged hours every day can compress sciatic nerve which passes beneath piriformis muscle and leads to piriformis syndrome, low back pain and self-inflicted sciatica.
The wallet acts as a wedge that forces the pelvis, spine and body out of alignment. Just as you would not sit on a brief case or a rock for an extended period of time, you should not sit on your wallet. Anyone who drives more than a half hour sitting on a wallet is a candidate for sciatica or back pain.
The healthiest option is to move the wallet to your front pocket. If it's must to keep your wallet in your back pocket, you should remove it before you sit